Inverters, and inverter based systems, are used in a variety of applications. By way of example, inverters are commonly used for converting direct current (DC) output from a photovoltaic (PV) solar array into alternating current (AC). This AC current can be supplied to the electrical grid, or used for other purposes, such as standalone electrical networks. Inverter operability, therefore, can be critical. Inverters, however, can be particularly vulnerable, and rendered inoperable, by a variety of different fault conditions.
When inverters become inoperable, especially when used in PV array energy systems, the result can be lost production, or worse: lost electrical generation. Solar applications inherently include large numbers of PV array circuits connected to a single inverter. These array circuits can have long cable runs (e.g., many kilometers), with many connection points, distributed to PV panels. These long cable runs increase the likelihood of faults, an increase the difficulty of identifying faults when they occur. Faults may also occur internal to the PV panels. Ground faults (e.g., line-to-ground) are among the most common type of faults
Given the long cable runs, large numbers of connection points, and the possibility of faults occurring within the PV panels, the chances of a ground fault outside of the inverter can be relatively high. In high power solar applications, the number of PV array circuits increases and the risks associated with downtime increases proportionally. Power inverters are conventionally used in these high power solar applications.
Power inverters typically operate on power circuits that are isolated from ground and sectioned off from other sources and loads. This is typically done when faults are detected to prevent common mode effects of the switching devices from affecting other loads and generation sources. Due to this isolation, a ground fault event can go undetected by other protection devices, such as fuses and circuit breakers, as a single fault will not usually activate these protection devices. Typically, line-to-ground faults are detected using conventional ground fault detection circuits.
These conventional devices, however, provide suboptimal fault tolerance. For example, conventional power inverters typically include a single circuit for detecting a fault on the entire power system without any indication of specifically where the fault is located. On the other hand, larger numbers of inverters can be used to provide more robust fault detection. These larger number of inverters come at considerably increased costs due to the higher number of systems and supporting infrastructure
Since the location of the faults cannot be easily determined in conventional systems, continued system operation of these systems, after the occurrence of faults, is nearly impossible.